Horizontal only texture blur?
The problem is mostly a result of aspect ratio of the zodiac image - ie, being much wider than it is tall.

Image Texture coordinates run from 0.0 - 1.0 in both the horizontal and vertical direction, regardless of the actual resolution of the image. Since the 'blur' acts on these image texture coordinates this means that the effect of the blur in one direction is much more pronounced than that in the other direction. To address this, you need to scale the texture coordinates before the 'blur' (in this case by a factor of 12) and 'un-scale' them after. This can be easily achieved by using Mapping nodes with the X-scale set to '12' and '1/12' respectively.



I also simplified the blur node as the original seemed to also introduce an offset.



This produces the following result :



Note that for this I also changed your mesh lights into Area Lamps. These produce better lighting and allow the number of samples to be considerably reduced with the same resultant quality.